Cutter inserts for machine and other tools may comprise a layer of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) bonded to a cemented carbide substrate. PCD and PCBN are examples of superhard material, also called superabrasive material, which have a hardness value substantially greater than that of cemented tungsten carbide.
Components comprising PCD are used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. PCD comprises a mass of substantially inter-grown diamond grains forming a skeletal mass, which defines interstices between the diamond grains. PCD material comprises at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa and temperature of at least about 1,200 degrees centigrade in the presence of a sintering aid, also referred to as a catalyst material for diamond. Catalyst material for diamond is understood to be material that is capable of promoting direct inter-growth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite. Some catalyst materials for diamond may promote the conversion of diamond to graphite at ambient pressure, particularly at elevated temperatures. Examples of catalyst materials for diamond are cobalt, iron, nickel and certain alloys including any of these. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. The interstices within PCD material may be at least partly be filled with the catalyst material. A disadvantage of PCD containing certain catalyst materials for diamond as a filler material may be its reduced wear resistance at elevated temperatures.
Components comprising PCBN are used principally for machining metals. PCBN material comprises a sintered mass of cubic boron nitride (cBN) grains. The cBN content of PCBN materials may be at least about 40 volume %. When the cBN content in the PCBN is at least about 70 volume % there may be substantial direct contact among the cBN grains. When the cBN content is in the range from about 40 volume % to about 60 volume % of the compact, then the extent of direct contact among the cBN grains is limited. PCBN may be made by subjecting a mass of cBN grains together with a powdered matrix phase, to a temperature and pressure at which the cBN is thermodynamically more stable than the hexagonal form of boron nitride, hBN. PCBN is much less wear resistant that PCD, which may limit its scope of application.
U.S. Pat. No. 7,516,804 discloses a superabrasive element comprising a mass of polycrystalline diamond including ultra-dispersed diamond grain structures present in an amount greater than zero weight percent and less than about 75 weight percent of the mass of polycrystalline diamond.
PCT publication number WO2009/147629 discloses a method for making PCD having an enhanced diamond contiguity and density.
There is a need for a polycrystalline superhard material having enhanced wear resistance, as well as a method for making it.